Galvanometer



AMM

Aug. 11,11959 y D. N. MONTGOMERY ETAL 2,899,641

GALVANOMETER Filed Jan. 17. 1957 Q INVENTORS. n DONALD M MONTGCMRY JACK L. 7`H0$`S` @Mw/ff@ ATTORNEYS dynamics Corporation, Pasadena, Calif., a corporation of California Application January 17, 1957, Serial No. 634,666

1 Claim. (Cl. S24-154) This invention relates fte improvements in galvanometers of the 'type adapted to respond rte alternating or oscillatin'g voltages. y

.A typical galvanometer of 'this type vc'or'nprises fa light- Weight fne -wire coil 'held in `suspension between a pair ofstr'etched l'wires or ribbons respectively anchored at `"opposite lends to an enclosed rgalvancmneter case. The suspension means delines the axis of rotary motion of the coil and supports a small mirror 'which is generally symmetrically-'arranged I'about this la'xi's and for deflection responsive to rotation of the coil. 1 A window .in the galvanometer case aligned with the mirror enables incidence and reflection of a light beam by the mirror .for sensing coil displacement.

The coil suspension means in ythe A'form of conductive wire or ribbon provides electrical leads to the coil, the

upper `(suspension means conventionally being anchored "to one terminal post sealed through an end ofthe galva- 'nomet'er case and providing one external contact. The lower suspension means is generally attached to ia-lo'wer .terminal member located at the-other end of thegalva- "no'rne'te'r case. "The A'suspension assembly, including lthe terminals, suspension members and the coil suspended between the suspension members, is electrically insulated from the case.

Itis a constant aim of those skilled in the art of making galvanometers to make the galvanometer as small as possible. The miniaturization of galvanometers provides many advantages in addition to the obvious advantage of light weight. Generally a plurality of galvanometers are set side-by-side in a recording instrument. Light rays incident upon the reflecting mirrors disposed within the galvanometers are deflected back to a photographic film and recorded as a plurality of separate traces, one trace for each galvanometer. A miniature galvanometer enables you to use a smaller camera and obtainmore traces upon a given width of iilm. Also, miniature galvanometers can be placed closer together than larger galvanometers, giving better linearity in the recorded signals.

This invention contemplates a galvanometer having certain features and structure which enable the construction of a small galvanometer. Galvanometers constructed in accordance with these features may be less than one inch in length and approximately sixty thousandths of an inch in diameter.

The invention contemplates suspending a ycoil of many turns of Wire within a galvanometer case. Instead of mounting the mirror to the suspension members, the mirror may be mounted upon the coil member. By mounting the coil in this manner the length of the suspension can be reduced, thus reducing the length of the galvanometer itself. The suspension assembly includes an upper terminal and a lower terminal of special construction, One of the terminals is constructed so as to be movable along the axis of the case. When adjustment of tension is required, `the movable terminal is adjusted VUnited States Patent "O g Avthe 4`wire back 'Ion zitself.

l 2,899,641 Patented Aug. 11, 1959 "ICC . longitudinally, yand Vthe tension on the 'suspension linembers varied.

The invention will be A'more clearly understood "with referen'ce to the 'accompanying drawings, iin which:

Fig. 1 is a sectional elevational view showing '.thenew galvanometer;

Fig. .2 Yris `an elevational view showing `the coil rand :mir- 'for assembly;

.Fig 3 is 'an enlarged .sectional view raken ralonglin'es 3&3 'of Fig. l; 'and yFig. 4 .is Aan enlarged sectional View taken along ky.lines 4&4 of Figli.

Referring toiiig. l which shows the galvanometer.'.in section 'and in elevation, a "casing 10 is provided .for enrc'lo'sing the suspension assembly. Thecasing .is elongated yin shape, having a length many times itsf'width. The :shape of the casing 1'0 may becylindrical Tor any'o'ther vshape to conform with 'the slots Vformed `-in magnet blocks, :into which galvanometers `of this type are usually placed.

An elongated coil .member12, consisting of many turns of wire, is suspended within the case l10 by an upper .suspension means 14 and :a lower suspension 4means 16.

v The kupper -an'd .lower 'suspension .means may be of round 1 wire yor of .ribbon which is rectangular 1in cross-section,

`rsired. 'A round wire suspension uis generally used-fora depending'uponV the resonant frequency-of the system lehigh frequency resonance, say above 1000 cyclesper isec- "The upper suspensionmember y14, the coil 1.2, andthe 'Suspension members 1=4 and 16 :are .fastened tothe v-coil yby ys'tirrlilr:connections 18 andl), respectively,

formed by passing the suspension wire throughtheopening of the coil and then soldering or otherwise connecting insulating bobbins -22 ,and 24 of suitably stili material are inserted into each end of the coil to provide support for the stirrup connections.

The open area of the coil 12, often called the window, is maintained at the proper dimension by the inclusion within the Window of `a reflecting mirror 26 shown more clearly in Fig. 2. The reilecting mirror can be directly bonded 4to the Wires of coil member 12 or, in the alternative, a stili insulating material can be bonded to the coil 12 and the mirror 26 mounted upon the insulating material.

A lens 28 is provided on the casing 10 adjacent mirror 26 so that incident light rays are directed to the mirror and reilected back through lens 28 to a recording medium (not shown).

Upper suspension member 14 is connected to a terminal 30. Lower suspension member 16 is connected to a terminal 32. Each of the terminals 30 and 32 is provided with extension members 34 and 3.6, respectively. The extension members 34 and 36 are offset from the axis of terminals 30 and 32. Extension member 34 is semicircular in cross-section, with the liat edge extending along the axis of terminal 30 (see Fig. 3). Extension member 36 is also semi-circular in cross-section, with its lilqat side extending along the axis of terminal 32 (see The upper suspension member 14 and the lower suspension member 16 can thus be bonded by ysoldering or any other suitable means to the ilat portions of extension members 34 and 36, respectively. This structure of the terminals permits the terminals, the suspension members 14 and 16, and the coil member 12 to be mounted within case 10 so that the axes of these members are along the axis of the case 10. Also, since the suspension members are mounted on the flat sides of the extension members, the length of the galvanometer is reduced The suspension members are insulated from the casing by means of an insulating member 38 and an insulating member 40 which electrically insulate the upper terminal 30 Iand the lower terminal 32 from the casing 10.

Provided in the lower portion of the galvanometer is a connector 42. A transverse hole is formed within the connector 42 into which is disposed a set screw 44. Set screw 44 is adapted to press tightly against terminal 32 when in the tightened position. t

The entire case is lled with an oil which has a high index of refraction to use the advantage of greater deections possible using the multiplying factor of the index of refraction, a well known principle. We prefer to use an oil having an index of reflection up to as high as four. An expansion tube 46 is disposed within a hole formed in the side of casing 10 to provide for the expansion of the oil under changes in temperature.

A support member 48 is located at one end of the galvanometer adjacent the upper terminal 30 and insulator 38. When the galvanometer is placed on the magnet block (not shown) the anges of the support member 48 rest upon the magnet block. Adjustment of the position of the galvanometer Within the magnet block can be made by the provision of holes 50 within the support member 48.

The galvanometer structure is assembled by rst connecting support member 48 rigidly to casing 10, and insulator 40 rigidly to casing 10 and connector member 42. Insulator 38 is then placed upon the upper extremity of casing 10 and upper terminal 30 cemented to the insulator 38.

Lower terminal 32, however, is movable. Therefore, lower terminal 32 can be moved axially within the casing 10 to adjust the tension exerted upon the suspension members. The tension adjustment is accomplished by loosening set screw 44, moving the terminal 32 in the proper direction to obtain the desired tension upon the suspension members, and then again tightening set screw 44.

We claim:

A miniature galvanometer assembly for operating in any relative position comprising a tubular case, a mounting flange member secured at one end of the case for supporting the case and having arcuate slots for permitting angular adjustment of the mounting flange and case, rst and second insulator members positioned in the respective ends of the tubular case, the insulator members having openings positioned along the longitudinal axis of the tubular case, a first terminal member extending through the opening in the rst insulator member into the interior of the tubular case, a second terminal member extending through the opening in the second insulator member into the interior of the tubular case, means including a set screw for adjustably securing the first terminal in the insulation member, a ilat elongated coil of wire, -a pair of electrically conductive suspension members respectively linking the ends of the elongated coil and being secured to the terminal members, the iirst terminal member being positioned and secured by the set screw to hold the coil and suspension members in tension, a mirror mounted on the coil, an oil having a high index of refraction completely filling the case, and an expansion tube connected to and communicating with the interior of the case, whereby all air bubbles can be removed from the case with the tube permitting Changes in the oil Volume with changes in temperature.

References Cited in the le of this patent UNITED STATES PATENTS 602,527 Sullivan Apr. 19,1898

730,061 Westen June 2, 1903 813,269 Wynne Feb. 20, 1906 1,981,266 Green Nov. 20, 1934 2,045,677 Schock June 30, 1936 2,268,526 Palmer Dec. 30, 1941 2,439,576 Morrow Apr. 13, 1948 2,469,265 Hathaway May 3, 1949 2,535,065 Heiland Dec. 26, 1950 2,599,661 Richardson June 10, 1952 2,622,118 Hendricks Dec. 16, 1952 

